1. Field of the Invention
The present invention relates to a waste liquid tank, a liquid ejection device, and an image forming apparatus.
2. Description of the Related Art
Some of printers, fax machines, copiers, plotters, and image forming apparatuses, which have some functions of these machines, form (record, or print) images by transferring liquid (hereinafter also referred to as “recording liquid” or “ink”) to a medium (the term “medium” as used herein is synonymous with the terms such as “medium to be recorded”, “recording medium”, “transfer material”, and “recording paper”, and is hereinafter referred to as “sheet” without limiting the material to paper) with use of, e.g., a liquid ejection device that comprises a recording head including a liquid ejection head for ejecting droplets of the liquid (recording liquid) while transporting the sheet.
The term “image forming apparatus” as used herein indicates a device that forms images by ejecting liquid onto media such as paper, strings, fibers, cloth, leather, metal, plastic, glass, wood, and ceramics. The term “forming images” as used herein indicates not only forming images that have meanings, such as characters and figures, on a medium, but also forming images that do not have meanings, such as patterns, on a medium. The term “liquid” as used herein is not limited to recording liquid and ink, but includes any material that is in the form of a fluid when ejected. The term “liquid ejection device” as used herein indicates a device that ejects liquid from a liquid ejection head and is not limited to that for forming images.
These types of liquid ejection devices and image forming apparatuses require mechanisms for maintaining and restoring performance of the liquid ejection heads for ejecting recording liquid. Primary functions of such a maintenance recovery mechanism for the head include a capping function for tightly sealing with a cap member so as to prevent recording ink near a nozzle head from being viscous and sticky due to natural evaporation of the ink, an ejection recovery function for discharging the recording ink so as to recover from ejection failures due to bubbles generated in a nozzle hole and for suctioning and discharging the recording liquid from the nozzle utilizing the capping function, and a wiping function for wiping off residual recording ink adhering to a nozzle face so as to prevent a variation of dispersion of droplets.
When head performance maintenance recovery operations are performed, recording liquid that has not been used for recording (image formation) is discharged as waste recording ink. Some apparatuses therefore include waste liquid tanks for holding such waste recording ink (called also as waste container, waste container unit, etc.) and fill-up sensors for detecting whether the waste liquid tanks are full.
For example, Patent Document 1 discloses provision of an absorbent material in a waste liquid tank. The absorption of waste recording liquid discharged into the waste liquid tank is increased by wetting the absorbent material with a waste liquid wetting liquid that is a substantially non-reactive liquid having a vapor pressure lower than about 20 mm of Hg at room temperature and comprising a hydrocarbon compound, thereby preventing formation of a mountain-like buildup of waste recording liquid. Especially when a hydrocarbon compound comprising a paraffin oil is used, the absorption of the waste recording liquid by the absorbent material is increased, formation of a mountain-like buildup of the waste recording liquid is more efficiently prevented.
<Patent Document 1> Japanese Registered Patent No. 3552790
Referring to Patent Document 2, a porous absorber impregnated with an ink coagulant of metallic salt is provided in a waste recording liquid tank. This coagulant is a metallic salt solution dissolved in an aqueous solvent.
<Patent Document 2> Japanese Patent Laid-Open Publication No. 10-119309
Patent Document 3 discloses reuse of waste recording liquid.
<Patent Document 3> Japanese Patent Laid-Open Publication No. 2003-326692
Patent Document 4 discloses a measuring device for measuring weight of functional liquid. The measuring device includes a receptacle filled with a functional liquid absorber for absorbing and holding the functional liquid ejected into the receptacle.
<Patent Document 4> Japanese Patent Laid-Open Publication No. 2004-177262
Patent Document 5 discloses a liquid ejection apparatus that comprises a receiving layer for receiving droplets and a diffusion layer for absorbing liquid in the receiving layer and diffusing the liquid, wherein the diffusion layer has a higher density than the receiving layer.
<Patent Document 5> Japanese Patent Laid-Open Publication No. 2004-155182
Referring to Patent Document 6, in order to recognize performance of droplets, a tank for collecting droplets is provided. Further, a liquid pump is provided for generating a suction force in the same direction as the ejection direction of the droplets and suctioning the droplets ejected from a head into the collection tank.
<Patent Document 6> Japanese Patent Laid-Open Publication No. 10-264411
Use of pigment inks including organic pigments, carbon black, etc., as colorant in current image forming apparatuses using inks is under study, or is being put into practice. Unlike dye, as the pigment is insoluble in water, the pigment is usually mixed with dispersant for dispersion treatment so as to be used as an aqueous ink containing the pigment stably dispersed in water.
Such a pigment ink generally has higher viscosity than dye inks, and has problems due to high viscosity. That is, waste of high-viscosity ink (waste recording liquid) tends to become more viscous, and if the viscous waste recording liquid is dropped on an absorbent member, the waste recording liquid is easily built up on the absorbent member without being absorbed therein.
As a result, waste recording liquid subsequently introduced into the waste liquid tank might slide on the buildup of the waste recording ink to flow out of the waste liquid tank. Moreover, the buildup might grow into a columnar shape to interfere with a liquid ejection head or a medium.
One solution may be, as disclosed in Patent Document 1, to wet the absorbent member with a waste liquid wetting liquid that is a substantially non-reactive liquid having a vapor pressure lower than about 20 mm of Hg at room temperature and comprising a hydrocarbon compound.
However, even with this configuration, if the waste recording liquid is frequently introduced into the waste liquid tank in high temperature and low humidity environments, or if the ink has high viscosity and quick drying properties, absorption of the waste recording liquid by the absorbent member does not keep up with introduction of the waste recording liquid, so that the amount of ink adhering to and built up on the surface of the absorbent member gradually increases and clogs pores of the absorbent member, resulting in forming a mountain-like buildup.
If, as disclosed in Patent Document 2, an aqueous solvent containing a wetting agent that has metallic salt reactive to ink dissolved therein is placed, the metallic salt aggregates through reaction with the ink, so that a mountain-like buildup of a waste recording liquid is more likely to be formed compared to the aqueous solvent not being placed in the waste liquid tank. Moreover, the waste recording liquid with aggregated color material has high viscosity and is not easily absorbed by a receptacle.